The Ruminant Nutrition System (RNS) is a comprehensive nutrition model that integrates cattle, sheep and goats into one platform. The RNS was developed to provide a framework that can be used for incorporating and implementing new scientific knowledge and submodels to more accurately predict nutrient requirements and biological values for ruminants currently used in food production. The RNS has a modern design and interface that uses an integrated object-oriented programming approach to allow for quicker and customized simulations. The RNS structure permits power users to expand their simulation routines through the R script programming.